From: Evgeniy Polyakov <[EMAIL PROTECTED]> Date: Wed, 26 Jul 2006 10:28:17 +0400
> I have not created additional DMA memory allocation methods, like > Ulrich described in his article, so I handle it inside NAIO which > has some overhead (I posted get_user_pages() sclability graph some > time ago). I've been thinking about this aspect, and I think it's very interesting. Let's be clear what the ramifications of this are first. Using the terminology of Network Algorithmics, this is an instance of Principle 2, "Shift computation in time". Instead of using get_user_pages() at AIO setup, we instead map the thing to userspace later when the user wants it. Pinning pages is a pain because both user and kernel refer to the buffer at the same time. We get more flexibility when the user has to map the thing explicitly. I want us to think about how a user might want to use this. What I anticipate is that users will want to organize a pool of AIO buffers for themselves using this DMA interface. So the events they are truly interested in are of a finer granularity than you might expect. They want to know when pieces of a buffer are available for reuse. And here is the core dilemma. If you make the event granularity too coarse, a larger AIO buffer pool is necessary. If you make the event granuliary too fine, event processing begins to dominate, and costs too much. This is true even for something as light weight as kevent. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
